What is a callback URL in relation to an API?
A callback URL will be invoked by the API method you’re calling after it’s done. So if you call POST /api.example.com/foo?callbackURL=http://my.server.com/bar Then when /foo is finished, it sends a request to http://my.server.com/bar. The contents and method of that request are going to vary – check the documentation for the API you’re accessing.